Syria's ambassador to Lebanon has vowed to retaliate for an Israeli air raid that hit a research centre on the outskirts of the capital Damascus on Wednesday.
According to Ali Abdul-Karim Ali, Syria "has the option and the capacity to surprise in retaliation" to respond to the "aggression of the Israeli warplanes".
He told Hezbollah-run news website Al Ahad that he could not predict when Damascus would take revenge. "Syria is engaged in defending its sovereignty and its land," he added.
Syrian military have dismissed claims that weapons have been shipped to the country, and said a scientific research facility outside Damascus was hit by the Israeli jets.
Reuters and AP reported that the target was a convoy carrying weapons for Hezbollah in Lebanon.
Iran, Syria's strongest ally in the region, has condemned the airstrike calling it a clear violation of Syria's sovereignty.
Hezbollah called the attack a "barbaric aggression" and said it "expresses full solidarity with Syria's command, army and people".
Russia echoed Iran's remarks, claiming it is taking "urgent measures to clarify the situation in all its details".
"If this information is confirmed, we have a case of unprovoked attacks on targets in the territory of a sovereign state, which grossly violates the UN charter and is unacceptable," Russia's foreign ministry said in a statement.
"Whatever the motives, this is not justified."
Earlier this week, Israel moved a battery of its new Iron Dome rocket defence system to the northern city of Haifa, near the border with the area of Lebanon controlled by the anti-Israel Hezbollah.
The fear, expressed by Israeli Prime Minister Benjamin Netanyahu, was that the militant group could exploit the civil war in Syria and snatch chemical and conventional weapons.